A liquid crystal panel using a polysilicon or CG (Continuous Grain) silicon substrate enjoys a better TFT characteristic than that using an amorphous silicon substrate.
The better TFT characteristic means higher electrical charge mobility, which makes it possible to monolithically mount, on the liquid crystal panel, circuits (a source driver, a gate driver, and the like) for driving the liquid crystal panel.
Usually, such a liquid crystal panel is a display panel composed of pixels arranged in a matrix (a matrix-type display panel). Other known matrix-type display panels include an EL (Electro Luminescence) panel and a plasma display panel.
The matrix-type display panels above are not capable of attaining an operating speed as high as that of an LSI because the transmission of signals via signal lines is delayed due to sizes (physical length) of the matrix-type display panels.
In order to overcome this drawback, some matrix-type display panels perform multi phase process at source drivers.
The “multi phase” is one form of parallel operation, in which each of video signals (R, G, and B) transmitted to the source driver is resolved into two to eight signals by such as serial-parallel conversion, and the resolved signals are transmitted through a plurality of video signal lines.
Because this processing reduces the amount of information (a frequency characteristic) per signal line, it is possible to easily increase the operating speed of the matrix-type display panel. Therefore, it is possible to attain, without interruption, a satisfactory display result even when the display signals (video signals) are those of a moving picture.
Moreover, for a matrix-type display panel, a technology has been developed as to lower resolutions in vertical and horizontal directions in order to increase the operating speed.
This technology is for simultaneously transmitting the same signal to adjacent source lines and adjacent gate lines by adding analog switches to the source driver or a gate driver.
Specifically, this technology makes it possible, for example, to transmit the same video signal to four pixels that are adjacent in the horizontal and vertical directions. By so doing, it is possible to increase the operating speed nearly four times faster. Moreover, it is also possible to reduce power consumption because the driving frequency can be reduced to one fourth if the operating speed is not changed.
Some display panels are capable of selectively performing a display operation in a low resolution mode, as described above, and in a high resolution mode in which all pixels receive different video signals so as to carry out display at high resolutions.
For example, Japanese Publication for Unexamined Patent Application, No. 64-18193, Tokukaisho (publication date: Jan. 20, 1989) discloses a technique for switching the high resolution mode and the low resolution mode of a display panel by switching connections of a source driver, using analog switches.
In this technique, a video signal or a data signal (display signals for a still picture) is supplied to each of four source lines via four bus lines. In the high resolution mode for still pictures, different data signals are respectively supplied to the four bus lines, while the same video signal is supplied to the four bus lines in the low resolution mode for moving pictures.
In this manner, this technique realizes a convenient way of providing the circuit with a function of switching the resolutions by adding the analog switches to the source driver.
However, the technique disclosed in the foregoing publication requires display signals to be supplied to all the bus lines, regardless of the resolution modes. This causes a problem that cost and calorific value cannot be reduced drastically, owing to the fact that power consumption can only be reduced to a limited extent in the low resolution mode.